#Filename: using_file.py

poem = '''\
Programming is fun
When the work is done
if you wanna make your work also fun:
    use Python!
'''

e = open('../poem.txt','w')
e.write(poem)
e.close()
new = []
f = open('../poem.txt','r+')
n = 0
for i in f.readlines():
    newline = "%d %s"%(n,i)
    new.append(newline)
    n += 1
f.close()
f =    open("poem_new.txt","w+")
f.writelines(new)

f.close()

解讀：1，開啟檔案格式，為寫，‘w’

2，每讀出一句，然後就把log 處理，加上行首，重新寫到新檔案。